With the rapid progress of image processing technology in recent years, not only stereoscopic image display apparatuses that generate stereoscopic images viewers can enjoy using special glasses having optical lenses, such as polarized lenses, but also stereoscopic image display apparatuses that generate stereoscopic images viewers can enjoy with the naked eyes are being developed in large quantities. In such conventional stereoscopic image display apparatuses, a stereoscopic image with respect to a single focus point is generated and displayed. Since some regions of a space can be recognized clearly, the spatial positional relationship can be recognized accurately. However, other regions are recognized as the so-called blurred images, and there occurs a problem of being difficult to accurately recognize the positional relationship in the entire region of the space.
FIG. 16 is a schematic view showing the concept of a conventional stereoscopic image display system. When a viewer sees the focus point 2 of a projected object (a vehicle in FIG. 16) via a screen 1 to which a stereoscopic image is projected, the stereoscopic image can be recognized clearly since no parallax occurs at the focus point 2. On the other hand, in the case of a stereoscopic image away from the focus point 2, as the parallax is larger, the divergence between the three-dimensional image 3 formed on the left retina and the three-dimensional image 4 formed on the right retina becomes larger, and the stereoscopic image is eventually recognized in a blurred state. FIG. 17 is a view showing regions in which image blurring occurs in the conventional stereoscopic image display system. As shown in FIG. 17, in the conventional stereoscopic image display system, fixed focal length lenses 5, 5, . . . are used, and the object near the focus point 2 can be recognized clearly. However, in regions away from the focus point 2, for example, in hatched regions 6, the parallax between the left and right images is larger than a predetermined value, and images are recognized as blurred images.
For the purpose of solving these problems, for example, in Japanese Patent No. 3064992 and Japanese Patent Application Laid-open No. 2001.238229, focus points are provided at multiple different positions between the viewer and the screen 1 using varifocal lenses, and the regions in which images can be visually recognized clearly are extended, whereby differences in the way how a stereoscopic image is seen depending on the differences in the position of the viewer, the focus point, etc. are equalized. FIG. 18 is a view showing regions in which image blurring occurs in a stereoscopic image display system incorporating varifocal lenses. As shown in FIG. 18, multiple focus points 2, 2, . . . , can be provided by using the varifocal lenses 7, 7, . . . . Furthermore, the hatched regions 6 in FIG. 17, that is, the regions in which the parallax between the right and left images is larger than the predetermined value and images are recognized as blurred images, can be reduced or eliminated by using the multiple varifocal lenses 7, 7, . . . and by ingeniously disposing the focus points 2, 2, . . . .